Carrier billing lets you pay for apps, music, or other digital purchases using...

https://post-wiki.win/index.php/Is_Pay_by_Phone_Billing_the_Same_as_a_Mobile_Wallet%3F

Carrier billing lets you pay for apps, music, or other digital purchases using your mobile phone account. Instead of using a credit card, the cost is added to your monthly phone bill or taken from your prepaid balance